Enzymes are protein with enormous catalytic activity. They are synthesized by biological cells and, in all organisms; they are involved in chemical reactions related to metabolism. Therefore, enzymes-catalyzed reactions also proceed in many foods and thus enhance or deteriorate food equality. Relevant to this phenomenon are the ripening of fruits, vegetables, meat and dairy products, and the processing steps involved in the making of dough from wheat or rye flours and the production of alcoholic beverages by fermentation technology.
Enzyme inactivation or changes in the distribution patterns of enzymes in sub-cellular particles of a tissue can occur during storage or thermal treatment of food. Since such changes are readily detected by analytical means, enzymes often serve as suitable indicators for revealing such treatment of food. Examples are the detection of pasteurization of milk, beer, or honey, and differentiation between fresh and deep frozen meat or fish.
Enzyme properties are of interest to the food chemist since enzymes are available in increasing numbers for enzymatic food analysis or for utilization in industrial food processing.
Details of enzymes that play a role in food science are restricted in this book to only those enzyme properties, which are able to provide an insight into the build-up or functionality of enzyme utilization in food analysis or food processing and storage.
In addition to an enzyme’s ability to substantially increase reaction rates, there is a unique enzyme property related to its high specificity for both the compound to be converted (substrate specificity) and for the type of reaction to be catalyzed (reaction specificity).
The substrate is specifically activated by the enzyme so that, among the several thermodynamically permissible reactions, only one occurs. Therefore, enzyme reaction specificity is considered as a basis for enzyme classification and nomenclature.
Enzymes are globular proteins with greatly differing particle sizes. Larger enzyme molecules often consist of two or more peptide chains arranged into a specific quaternary structure.
Most of enzyme properties are clearly and reliably revealed only with purified enzymes. Prerequisites for the isolation of a pure enzyme are selected protein chemical separation methods carried out at 0-4 degree Celsius since enzymes are often not stable at higher temperatures.
Chromatographic separations of an enzyme can occasionally result in separation of the enzyme into iso-enzymes, i.e. forms of the enzyme, which catalyze the same reaction although they differ in their protein structure.
The catalytic activity of enzymes is exhibited only under specific conditions, such as pH, ionic strength, buffer type, presence of cofactors and suitable temperature.
Rigorous analysis has demonstrated that numerous enzymes are not pure proteins. In addition to protein, they contain metal ions and/or low molecular weight non-protein organic molecules. These non-protein hetero constituents are denoted as cofactors.
Enzymes are substantially better catalysts than are protons or other ionic species used in non-enzymatic reactions. Enzymes invariably surpass all chemical catalysts in relation to substrate and reaction specificities.